This invention relates to 2-hydroxy-4-alkoxybenzophenone ultraviolet radiation absorbing compounds, to a process for preparing such compounds, to synthetic resins stabilized against the harmful effects of ultraviolet radiation by incorporating in such resins small quantities of such compounds, and to stabilizer compositions comprising such compounds in combination with a known polymer stabilizer.
Certain 2-hydroxy-4-alkoxybenzophenone compounds are known to be effective ultraviolet absorbers and light stabilizers, with the 2-hydroxyl group critically necessary for effectiveness. There are among a large number of classes of compounds disclosed in the patent literature as meeting the requirements for an effective ultraviolet radiation absorber. In lieu of individual references, the review by G. R. Lappin in "Encyclopedia of Polymer Science and Technology" (N. Bikales, ed. New York, John Wiley-Interscience, 1971) Vol. 14, pages 125 to 148 can be consulted.
According to Lappin's review, the 18 2-hydroxybenzophenone compounds indicated to be in commercial use as stabilizers are low to moderate molecular weight compounds having a single benzophenone unit in the molecule. Lappin refers to problems of "compatibility" of the additive stabilizer with the polymer being stabilized, including such properties as the solubility of the additive in the polymer, the rate of diffusion of the additive through the polymer, and the rate of loss of the additive from the polymer. Lappin characterizes compatibility as "a sensitive function of molecular structure and not entirely predictable". Among attempts to improve on the commercially available 2-hydroxybenzophenones, Lappin indicates that longer outdoor life of polymers might be obtained with relatively high molecular weight ultraviolet radiation absorbers and states that attempts to utilize polymeric and polymerizable absorbers for this purpose had given ambiguous results and not been commercially successful.
Subsequent attempts to overcome the inadequacies of the conventional ultraviolet absorber stabilizers include a number of disclosures of 2-hydroxybenzophenones having either a plurality of benzophenone units in the molecule or functional group substitution in addition to hydroxyl and alkoxyl. Thus Lappin in U.S. Pat. No. 3,310,525 of March 21, 1967 disclosed alpha-omega-bis(2-hydroxybenzoyl)alkane stabilizers for polyesters and poly-alpha-olefin resins, having a formula ##STR1## wherein n is an integer in the range from 2 to 8, and X, Y and Z are independently selected from the group of hydrogen, C.sub.1 -C.sub.4 alkoxy and C.sub.1 -C.sub.4 alkyl radicals.
H. Dressler in U.S. Pat. No. 3,399,237 of August 27, 1968 disclosed ultraviolet light stabilizing derivatives of 4-benzoylresorcinol having the formula ##STR2## wherein Z is a member selected from the group consisting of sulfur and ##STR3## and R is a member selected from the group consisting of hydrogen and alkyl having from 1-11 carbon atoms.
M. Minagawa in Japan Kokai 74 78,692 of July 29, 1974 disclosed 2-hydroxybenzophenone derivatives carrying cyclic imide substituents linked to the 4-position of the 2-hydroxybenzophenone by an alkyleneoxy group, for example 4-(2-phthalimidethoxy)-2-hydroxybenzophenone.
M. Minagawa in Japan Kokai 75 74579 of June 19, 1975 disclosed 2-hydroxybenzophenone derivatives having from 2 to 7 hydroxybenzophenone units linked through such bivalent groups as methylene, methyleneoxymethylene, cyclohexylidene, sulfide, sulfinyl, sulfonyl, alkylidene, carboxyalkylidene, and carbalkoxyalkylidene, including for example methylenebis(2-hydroxy-4-methoxybenzophenone). The location of attachment of the bivalent linking group on the 2-hydroxybenzophenone unit is nowhere specified by Minagawa.